The present invention relates to an external synchronizing method and apparatus for synchronizing a plurality of transmitters in an information transmission system to each other.
In a monitor television (TV) system which is one of information transmission systems available today, a plurality of remote TV cameras are switchably connected to at least one TV monitor by a transmission line. One is allowed to observe images picked up by any one of the TV cameras on the TV monitor by switching operations because information signals inclusive of image signal components are delivered from the respective cameras to the monitor over the transmission line. The prerequisite in this kind of information transmission system is that synchronization be set up between the cameras, or transmitters, in order to prevent the image on the monitor, or receiver, from being disturbed just after switching the cameras from one to another.
Synchronization between the transmitters is usually implemented by sync signals which are generated by an external sync signal generator. The sync signals, or external sync signals, have customarily been distributed to each transmitter over an exclusive external sync signal line which is independent of the transmission line adapted for the delivery of information signals from the transmitter to the receiver. The problem with the prior art transmission system is, therefore, that the transmission line and the external sync signal lines extending in parallel with the transmission line make the wiring of the system extremely intricate.